Siloxanes are chemical compounds composed of units of the form of R2SiO, where R is a hydrogen atom or a hydrocarbon group. They belong to the class of organosilicon compounds. Siloxanes can have branched, unbranched or cyclic backbones consisting of alternating silicon and oxygen atoms [—Si—O—Si—O—], with side chains R attached to the silicon atoms. The word siloxane is derived from the words silicon, oxygen, and alkane.
Polymerized siloxanes with organic side chains (R≠H) are commonly known as silicones or as polysiloxanes. Representative examples are [SiO(CH3)2]n (polydimethylsiloxane) and [SiO(C6H5)2]n (polydiphenylsiloxane). These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the —Si—O—Si—O— backbone is purely inorganic.
Hydrosilylation is a reaction widely used in the silicone industry for the preparation of monomers with silicon-carbon bonds and for crosslinking of siloxane compounds. Frequently, vinyl-terminated siloxanes and hydrosiloxanes (i.e. compounds containing a Si—H bond) are reacted in an addition cure mechanism to form siloxane polymers (polysiloxanes). The hydrosilylation and polymerization reactions are catalyzed by highly active platinum catalysts, such as the well-known Karstedt catalyst, which is prepared by the reaction of chloroplatinic acid with divinyl-tetramethyldisiloxane [CH2═CH—Si(CH3)2—O—Si(CH3)2—CH═CH2] in the presence of an alcohol and a base. This catalyst, Pt-divinyl-tetramethyldisiloxane (also abbreviated Pt—VTS) contains Pt in the oxidation state 0 and is commercially available and widely used in the silicone industry, in particular for Pt-catalyzed addition polymerization.
The so-called Ashby catalyst is based on the Pt-tetravinyl-tetramethyl-cyclotetrasiloxane complex and can be depicted by the formula Pt(CH2═CH(Me)SiO)n (wherein n=3, 4). This catalyst is commercially available under the name platinum cyclovinylmethylsiloxane complex and is registered under the CAS Registry Nr. 68585-32-0. In the present application, it is hereinafter abbreviated as “Pt—CS”.
Only a few Pt siloxane compounds are known, in which carbon monoxide (CO) is bonded directly to the platinum atom.
In U.S. Pat. No. 3,865,858, the reaction products of dicarbonyl-dichloroplatinum (Pt(CO)2Cl2) with 2,4,6,8-tetra-ethenyl-2,4,6,8-tetramethylcyclotetrasiloxane are described. They are used as catalysts for the production of organosilicon compounds.
Further, a compound is commercially available under the name platinum carbonyl cyclovinylmethylsiloxane (“Ossko's catalyst”) from different vendors. It is registered as a reaction product of Pt(CO)2Cl2 with cyclotrisiloxane (ref to CAS Registry No. 73018-55-0). There is no specific formula published for this compound.
The compound platinum carbonyl [2,4-di(η-2-vinyl)-6,8-diethenyl-2,4,6,8-tetramethylcyclotetrasiloxane] is registered under CAS Registry No. 226921-57-9. This compound has the formula C13H24O5PtSi4 and the structure is given in CAS (Formula I) does not differentiate between stereoisomers. Pt is present as Pt(0) in the oxidation state 0:

In JP2002-30185 a compound is cited with the short formula Pt(CO)[CH2═CH(Me)SiO]4 under the name Pt(CO)-2,4,6,8-tetraethenyl-2,4,6,8-tetramethyl-cyclotetrasiloxane. JP2002030185 further describes the use of this Pt compound as a catalyst for crosslinking rubber compositions which comprise a Si—H group containing compound and a non-conjugated polyene copolymer. However, no details as to the exact structure and to the preparation process of the Pt-catalyst are given.
CAS Registry Nos. 1269667-88-0 and 1269667-86-8 (registered Mar. 23, 2011) describe Pt carbonyl-tetramethyl-cyclotetrasiloxanes with cis- and trans-configurations of the vinyl groups bonded to the Pt atom.